The present invention relates to a method and apparatus for multi-image formation in electrophotography and electrostatic recording process.
Electrophotography and electrostatic recording method were developed in order to reproduce information faithfully and speedily. Thereafter, the efforts of improving electrophotography and electrostatic recording method have been directed at making a clearer copy than the original document and reproducing the original at a high speed by copying selectively a necessary portion out of the original document. Making a clearer copy than the original or reproducing only a necessary portion of the original differs from the original object of electrophotography and electrostatic recording method for reproducing the original as faithfully as possible. Such a difference comes from the efforts of making the reproduced information more valuable. In other words, the efforts of making the reproduced information more valuable give rise to such a difference in the object of electrophotography and electrostatic recording method.
Reproducing a more valuable information signifies reproduction of a new information and a creation of information.
If a copying apparatus could make not only reproduction of an original, but also a creation of new information, that would be epoch-making. A new original can be prepared by clipping the original and by use of the conventional copying apparatus. However, this is not a creation of new information by the copying apparatus, but a manual creation of the original. A creation of information by copying apparatus signifies eliminating an unnecessary information from the original or adding new information to the original during the image formation process of copying apparatus.
The creation of information by copying apparatus can be attained by synthesizing images. In synthesizing images, it would be expedient to synthesize images at the step of a latent electrostatic image formation rather than synthesizing visible images. In the conventionally known synthesis of latent electrostatic images, on a first latent electrostatic image formed on a photoconductor by projecting a light images upon the photoconductor is superimposed a second latent electrostatic image which is formed from a light image or by a laser beam.
In the case where the first latent electrostatic image is a positive image, namely when the potential of an image area is higher than that of background, a second latent electrostatic image cannot be formed in the background area since the background does not have a sufficient potential.
On the other hand, if it is tried to form a second latent electrostatic image on the image area having a sufficient potential for forming a latent image, the image of the first latent electrostatic image will be destroyed and the second latent electrostatic image will not be formed accurately. Therefore, in the conventional method, the first latent electrostatic images is formed as a negative image in which the potential of an image area is low and the potential of background is high, and a negative second latent electrostatic image is formed on the background, so that a positive visible image is obtained by a reversed development method.
However, ordinary original documents mostly have positive images and it takes a special apparatus to form negative latent electrostatic images from the positive images. Therefore, an image overlapping process tends to become complicated.